1. Field of the Invention
The present invention relates to electromagnetic surface waves, and in particular, to a system and a method of surface wave imaging to map pressure on a surface.
2. Description of Related Art
A conventional method of measuring surface pressure is to apply pressure taps or transducers to the surface, but these approaches have some significant disadvantages. Taps and transducers only allow measurements at discrete points on the surface. The surface pressures at other locations can only be interpolated from the known points. Another disadvantage is that taps and transducers are intrusive to the flow. Measurements cannot be taken downstream of other taps or transducers, since the flow is altered once it passes over the upstream disturbances. Finally, taps and transducers are time-consuming and expensive to use. Determining surface loads in aircraft design typically cost $500,000 to $1 million, with approximately 30% of that cost going towards the pressure taps and their installation.
Another method of measuring surface pressure utilizes pressure sensitive paint (PSP). PSP is essentially a luminescent dye dispersed in an oxygen permeable binder. The dye is excited by absorbing UV light; it then emits visible light. The intensity of the emitted light is dependent on the pressure of oxygen in the surrounding atmosphere. As the pressure of the oxygen above the PSP increases, the intensity of the emitted radiation will decrease. PSP provides a much greater spatial resolution than pressure taps, and disturbances in the flow are immediately observable. PSP also has the advantage of being a non-intrusive technique, since it does not affect the air flow across the surface.
PSP has the following disadvantages. 1) PSP coating degrades with time; 2) PSP response is temperature dependent; and 3) It requires excitation by an external source of UV, is only used in a controlled laboratory environment, and can't be used as a real time diagnostic.
Due to the disadvantages of using pressure taps to measure pressure on a surface and the undesirable characteristics of PSP, a need exists for an improved system and method for measuring pressure on a surface.